Transcriptional regulation of tendon differentiation and matrix formation

描述（由申请人提供）：肌腱将肌肉收缩产生的力传递给骨骼，通过坚固和高度组织的胶原原纤维束，建立肌腱的生物力学特性。在肌腱中，细胞扩展吞噬胶原原纤维束，并为原纤维生长产生微环境。肌腱中胶原原纤维的生长是决定肌腱生物力学性能和抗拉强度的最重要因素。胶原原纤维的生长分为两个阶段，在胚胎阶段，原纤维组装缓慢，在出生后阶段，原纤维的生长速度更快，可能通过原纤维融合发生。然而，我们对调控这些过程的基因程序一无所知。我们之前已经证明bHLH转录因子sclaxis对早期肌腱分化至关重要，并且它可能在胶原纤维形成中也起重要作用。在第二个肌腱转录因子的突变，莫霍克，我们现在发现胶原纤维生长的后期出生阶段的失败。本项目主要研究sccleraxis和Mohawk蛋白在胶原纤维形成和肌腱成熟中的作用。第一个具体目标是关注胚胎肌腱中的肌腱组装，第二个目标是关注出生后阶段肌腱成熟和胶原纤维快速生长的调节。这两个阶段将采用类似的方法处理这些进程。正常肌腱生长和肌腱表型将首先通过一组增强的结构参数进行评估，并检查Scx或Mkx过表达对肌腱生长的影响。sccleraxis和Mohawk功能的分子介质将通过微阵列分析鉴定，少数靶基因的调控作用将通过转基因拯救Scx或Mkx表型来确定，将单个或多个靶基因的表达重新引入突变背景。我们最近确定了ZFP185，一种锌指转录因子，作为我们计划进行转基因救援的第一个有希望的候选者。确定控制纤维生长的调控途径可能有助于在临床环境中加强和调节这些过程。

DESCRIPTION (provided by applicant): Tendons transmit the force generated by muscle contraction to the skeleton, through robust and highly organized bundles of collagen fibrils that establish the biomechanical properties of tendons. In the tendons, cellular extensions engulf bundles of collagen fibrils and generate the microenvironment for fibril growth. Growth of the collagen fibrils in tendons is the single most significant factor that determines biomechanical properties and tensile strength of tendons. Collagen fibril growth occurs in two phases, slow fibril assembly in embryonic stages and a much faster pace of fibril growth that likely occurs through fibril fusion in postnatal stages. Nothing, however, is known about the genetic program that regulates these processes. We have previously shown that the bHLH transcription factor Scleraxis is essential for early tendon differentiation and that it likely also plays an important role in collagen fibrillogenesis. In mutants of a second tendon transcription factor, Mohawk, we now find a failure of the later postnatal phase of collagen fibril growth. This project focuses on the role of Scleraxis and Mohawk in collagen fibrillogenesis and tendon maturation. The first specific aim focuses on tendon assembly in embryonic tendons and the second aim looks at the regulation of tendon maturation and rapid collagen fibril growth in postnatal stages. These processes will be addressed following a similar approach in both stages. Normal tendon growth and tendon phenotypes will initially be evaluated with an enhanced set of structural parameters and the effects of overexpression of Scx or Mkx on tendon growth will be examined. Molecular mediators of Scleraxis and Mohawk functions will be identified by microarray profiling and the regulatory roles of a small number of target genes will be determined by a transgenic rescue of the Scx or Mkx phenotypes reintroducing the expression of a single or multiple target genes into the mutant background. We recently identified ZFP185, a Zinc Finger Transcription factor as the first promising candidate for which we plan to proceed with a transgenic rescue. Identifying regulatory pathways that control fibril growth will likely contribute to the ability to enhance and regulate these processes in clinical settings. PUBLIC HEALTH RELEVANCE: Sports and age related tendon or ligament injuries are of the most common causes for orthopedic treatments and the long healing periods for these injuries translate to considerable hardship to the affected individuals and a significant economic burden for society. The capacity to return these tissues to their original strength is tightly linked to the quality of the collagen matrix that develops in the treated tissue. Considerable attention has therefore been directed to the proteins that make up the collagen fibrils in tendons and to the extracellular proteins that regulate fibril growth. Nothing however is known about the higher levels of regulation of these processes. The long term goal of this project is to decipher the transcriptional network that governs collagen fibrillogenesis and fibril growth in tendons and ligaments. Identifying the key regulatory players in this process is likely to open new avenues for enhancement of the clinical outcomes of tendon and ligament injury or replacement.